Senators worried about rising gasoline prices Wednesday asked the Government Accountability Office to update a two-year-old study that found mergers in the petroleum industry accounted for a small but significant hike in prices at the pumps.

The move could renew disagreements between GAO and the Federal Trade Commission, which must approve petroleum industry mergers. When the 2004 report was released Tim Muris, then the FTC chairman, complained that the report’s conclusions were unsound.